Heliolisk was easily in the top 5 best designed Gen 6 mons. The fact that it isn't Electric/Dragon is the only thing wrong with it. Regardless, its in my top 20 mons for sure. I hope they change its typing later on like they did with all the fairies.

Basically, from what I get by your idea.
Is by absorbing kinetic energy your body becomes denser, to compensate your body shrinks until you release the energy, in which your body returns to normal size.
I wouldn't go so far as ant-man but something like shrinking to a foot high and you weigh something like 10 Ton.

I get the density increase, but why does the weight increase aswell? Unless you somehow store the energy you absorb in the form of mass. Even then, a hit making you 10 tons would be extremely powerful.